SURFACE-MEMBRANE POLYPEPTIDES ASSOCIATED WITH HEMOCYTES FROM SCHISTOSOMA MANSONI-SUSCEPTIBLE AND MANSONI-RESISTANT STRAINS OF BIOMPHALARIA-GLABRATA (GASTROPODA)

Previous studies have shown that hemocytes from inbred susceptible and resistant strains of the snail, Biomphalaria glabrata, differentially react to primary sporocysts of the blood fluke, Schistosoma mansoni. It has been hypothesized that this differential reactivity may be due to differences in the expression of hemocyte surface determinants serving as parasite recognition and/or hemocyte activating factors. In order to begin addressing this hypothesis the hemodynamics and surface polypeptides of circulating hemocytes from susceptible and resistant B. glabrata strains were compared in two morphologically distinct cellular subpopulations that differed in their substrate adherence properties. When compared to a S. mansoni-resistant snail strain, two susceptible strains exhibited overall lower total circulating cell numbers and a consistently lower proportion of nonadherent hemocytes. Exposure of snails to S. mansoni miracidia induced significant increases in total circulating cell number in all strains by 2 days postexposure (PE). However, the proportion of adherent and nonadherent hemocytes remained constant in each snail strain at 2 and 4 days PE. A sensitive technique involving biotin labeling of polypeptides at the surface of living hemocytes, followed by nonreducing SDS-PAGE separation and electrotransfer to nitrocellulose, revealed a similar pattern of hemocyte surface polypeptides ranging in apparent molecular weights from 210 to 30 kDa in the three B. glabrata strains. One exception was the presence of 66-kDa polypeptide expressed at the surface of both adherent and nonadherent hemocytes in the two susceptible snail strains, which was only weakly expressed or absent from hemocytes of the resistant 13-16-R1 B. glabrata strain. In addition, exposure of snails to S. mansoni miracidia appeared to modulate (enhance) expression of the 66-kDa polypeptide in susceptible B. glabrata cell populations. Although the functional importance of this membrane polypeptide is unknown, the differential enhancement of expression in susceptible vs resistant snail hemocytes may reflect potentially important biochemical changes related to previously observed strain-specific reactivities to invading larval S. mansoni. Finally, a complex of high-molecular-weight surface polypeptides (approx 210 kDa) associated with adherent hemocytes was consistently reduced or absent in nonadherent cell preparations suggesting a possible role in substrate adhesion. © 1994 Academic Press. All rights reserved.